Method for transmitting signals in a radio communications system

ABSTRACT

According to the invention, a message belonging to a protocol is signalled by a base station subsystem (BSS) in a radio communications system to user equipment (UE), said message consisting of at least one message element. The changes to the message elements in comparison to an older version of the message are signalled at the beginning of the message.

[0001] The invention relates to a method for signal transmission in aradio communications system. The invention is particularly suitable foruse in a mobile radio or wire-free subscriber access system.

[0002] In radio communications systems, for example thesecond-generation European mobile radio system GSM (Global System forMobile Communications), information (for example speech, pictureinformation or other data) is transmitted by means of electromagneticwaves via a radio interface. The radio interface relates to anconnection between a base station and subscriber stations, in which casethe subscriber stations may be mobile stations or fixed-position radiostations. The electromagnetic waves are in this case emitted at carrierfrequencies which are in a frequency band that is intended for therespective system. Frequencies in the frequency band around 2000 MHzhave been provided for future radio communications systems, for examplethe UMTS (Universal Mobile Telecommunication System) or otherthird-generation systems. Two modes are envisaged for the thirdgeneration of mobile radios, with one mode being referred to as the FDDmode (Frequency Division Duplex), and the other mode being referred toas the TDD mode (Time Division Duplex). These modes are each used indifferent frequency bands. Both modes support a so-called CDMA (CodeDivision Multiple Access) subscriber separation method.

[0003] One important factor in the development of mobile radio systemsis to ensure that each new version of a protocol is compatible witholder versions. This ensures in particular that more recent subscriberterminals can be correctly identified and addressed in an environment ofbase stations which support an older protocol version and, conversely,the subscriber terminals which support an older protocol version stilloperate correctly in new network environments. However, this is notintended to prevent the existing messages at the control level between asubscriber terminal and base station from being expanded in order tosupport new services or features. For this purpose, all the signalingmessages must provide a type of expansion mechanism in order that thesame message may in more recent versions of the protocol include newelements, without this adversely affecting the functionality of “old”receivers.

[0004] In the case of these new expansions, a distinction is drawn inthe described UMTS mobile radio system, by way of example, betweencritical and non-critical expansions. If the receiver of a messageidentifies a new element which it cannot decode (since, for example, itis defined in a newer version which the receiver does not yet know) andthis element is identified as being critical, it should reject themessage as being incomprehensible. The transmitter uses this rejectionto deduce that the receiver supports an older version of the protocol,and the message is repeated without the additional elements of the newversion. If the receiver sees an unknown element which is identified asbeing non-critical in the message, then it should ignore this elementand attempt to decode the rest of the message correctly. When developingexpansion mechanisms, it is important to minimize the necessary messageoverhead, and to ensure that it is possible to switch to the correctprotocol version (the latest which both ends can understand) with theminimum delay.

[0005] Solutions with respect to expansions of communications protocolshave been proposed for two problems:

[0006] Problem 1:

[0007] In the case of the communications protocols (for example in theradio resource part) which are known from the prior art for the GSM andUMTS mobile radio system, expansion mechanisms are implemented byreserving space at the end of a message, which can be filled withexpansions and which may, for example, also have a so-called flag(indicator) (for example for UMTS) that the expansion has beenidentified as being critical or non-critical. This has the disadvantagethat the messages become larger with each new version, since there areno mechanisms to shorten the message, that is to say elements from olderprotocol versions cannot be removed. The current expansion is thusalways at the end of the previous version.

[0008] Problem 2:

[0009] If a subscriber terminal receives a message with a criticalexpansion (for example in the case of UMTS) which it does notunderstand, then the entire message is rejected and the network makesanother attempt, using the same message but with an older version of theprotocol. When selecting the older version of the message, the networkcannot, according to the prior art, make use of any informationwhatsoever about protocol versions which the subscriber terminal doesunderstand. The simplest solution for a network would thus be to use theoldest version of the protocol, for which the network can assume thatevery subscriber terminal supports it. However, this means that thelatest version, which the subscriber terminal could support, would neverbe used. A further option would be to in each case always send the nextolder version of the message to the subscriber terminal. If necessary,this procedure might have to be repeated more than once, for example ifthere is a large version difference between the transmitter and thereceiver, and this can lead to a considerable delay in the protocolsequence.

[0010] The invention is based on the object of specifying a method whichallows simplified protocol matching between components in a radiocommunications system.

[0011] This object is achieved by the methods and by the base stationsystem as claimed in the independent patent claims. Advantageousdevelopments of the invention can be found in the dependent patentclaims.

[0012] The described method according to the invention is usedparticularly advantageously in a radio communications system which is inthe form of a mobile radio system or wire-free subscriber access systemand which, in particular, uses a TDMA and/or CDMA subscriber separationmethod.

[0013] Exemplary embodiments of the invention will be explained in moredetail with reference to the attached drawings, in which:

[0014]FIG. 1 shows a block diagram of a radio communications system,

[0015]FIG. 2 shows one possible implementation of protocol expansions,if these are possible only at the end of the previous version, and

[0016]FIG. 3 shows a further possible implementation of protocolexpansions.

[0017]FIG. 1 shows a part of a mobile radio system as an example of thestructure of a radio communications system. A mobile radio system ineach case comprises a large number of mobile switching centers MSC,which are part of a switching network (SSS—Switching Subsystem) and arenetworked to one another, and/or produce access to a landline network,and in each case one or more base station systems BSS (BSS—Base StationSubsystem) which are connected to these mobile switching centers MSC. Abase station system BSS in turn has at least one device RNC (RNC—RadioNetwork Controller) for assigning radio resources, as well as at leastone base station NB (NB—Node B), which is in each case connected to it.

[0018] A base station NB can set up connections via a radio interface tosubscriber stations UE (UE—User Equipment) Each base station NB forms atleast one radio cell Z. The size of the radio cell Z is generallygoverned by the range of an organization channel (BCCH—Broadcast ControlChannel) which is transmitted by the base stations NB at an increasedand constant transmission power level. In the case of sectorization orin the case of hierarchical cell structures, each base station NB mayalso supply a number of radio cells Z. The functionality of thisstructure can be transferred to other radio communications systems inwhich the invention may be used.

[0019] The example in FIG. 1 shows two subscriber stations UE which arelocated in the radio cell Z of the base station NB. The subscriberstations UE have each set up a communications link to the base stationNB on which signal transmission for a chosen service is taking place inthe uplink direction UL and in the downlink direction DL. Thecommunications links are separated, for example, by different spreadcodes (CDMA codes) being allocated to the subscriber stations UE.

[0020] During the connection, the subscriber stations UE and the basestation NB still evaluate transmission characteristics of the radiointerface periodically, by means of a channel estimate.

[0021] In order to solve the problem 1 as described in the introduction,the invention proposes that the number of critical changes contained inthe message be signaled right at the start of the message. Any changemay in this case comprise expansions in the previous sense, or else mayinclude removing or changing already existing elements. One advantage ofthis method is that the receiver does not have to start decoding themessage when it identifies that the start of the message containsunknown critical elements, which leads to rejection of the message. Inaddition, this method has the advantage that the new message is notlinked to the structure of the old message, and there is therefore nolonger any need to transmit elements that are no longer required.

[0022] The non-critical expansions may, according to the prior art, belocated at the end of the message since, in this case, the message isnot rejected, and therefore the start of the message must be decoded inany case. Thus, overall, the message comprises three parts. The firstpart is an integer which indicates how many critical changes have beenimplemented in this message since the first version of the protocol.This number may be coded, for example, using any desired (binary) codingwhich satisfies a so-called Fano condition (there is no code word at thestart of another code word). The second part contains the currentversion of the message (as it is identified on the basis of thecorresponding number of changes). The third part contains one or morenon-critical expansions. Before each of these expansions, one bitsignals that another is still to follow, and one bit after the lastsignals that this was the last.

[0023] Accordingly, the process of identifying the expansions, whichuntil now has been distributed over all the changed message elements, isnow drawn to the start of the message. The bit sequence is then usedeither directly as a version code, or may be additionally codedsubsequently, as well. The advantage is firstly that the receiver canimmediately identify at the start of the decoding process whether itwill understand this version. Furthermore, there is no longer any needto leave the previous version unchanged, for example an element whichhas been replaced in the meantime can also be deleted.

[0024] The following proposal has been made in order to solve theproblem 2 as described in the introduction. If expansion mechanisms areimplemented by using expansion bits, then these expansion bits can beinterpreted as version numbers of the message. The receiver can use therejection message to signal how many expansions it can identify in themessage, as a maximum. The transmitter can in consequence select thecorrect version of the message straight away on the next attempt,without having to try out all the intermediate versions.

[0025] A further option is to insert a so-called identifier of aninformation element of the latest version of the message in therejection message. The invention proposes that this information elementidentifier be used for identification of one version of a message.

[0026] A third option is to insert version numbers of the messages,which are used only for the rejection message, explicitly in theprotocol.

[0027] The inventive step is that information relating to criticalexpansions to a message is transmitted right at the start, so that eachversion of a message can be given a completely new structure. Incontrast to methods where the protocol version is transmitted at thestart of the message, each message is in this case individually given aspecific version, so that the version counter is not incremented for allmessages, but only for those messages which have also actually beenchanged.

[0028] The insertion of a version identification in the rejectionmessage makes it possible to efficiently inform the network of theversions of a message that are supported.

[0029] According to the invention, the receiver will not only reject anincomprehensible version of a message, but will explicitly inform thetransmitter of which version it does support. This avoids possiblyunnecessary protocol operations, since the transmitter can use the“correct” version directly for the second attempt.

[0030]FIGS. 1 and 2 are intended to illustrate the method according tothe invention. In this case, a message is considered in a protocol whichcontains two elements in the first version 1a (element1 and element2).The message has an additional element (element3) in the second version1b, but this is not critical and can be ignored by a receiver which isusing the older protocol version. In the third version 2, a criticalelement is attached (element4), the first element (element1) has beenchanged (element1a), and the third element (element2) is no longer used.

[0031]FIG. 2 shows the three versions of the messages for the situationwhere expansions can be inserted only at the end of the protocol, forexample as will be possible on the basis of the current status of theUMTS standardization in the RRC (Radio Resource Control). In comparisonto this, FIG. 3 shows the messages according to the concept on which theinvention is based.

[0032] It is also possible to use the solution to the described problem2 in this case. If a subscriber terminal which supports only version 1aof the message receives a higher version, then it can use the twoexpansion bits as an identification of the supported message version.

[0033] The version number for version 1a is in this case 00 (KE=0,NE=0).

[0034] The version number for version 1b is in this case 010 (KE=0,NE=1, NE=0)

[0035] The version number for version 2 is in this case 11000 (KE=1,NE=1, NE=0, KE=0, NE=0).

[0036] Alternatively, it is also feasible to use only the criticalexpansion bits as the basis.

[0037] The version number for version 1a is in this case 0 (KE=0).

[0038] The version number for version 1b is in this case 0 (KE=0).

[0039] The version number for version 2 is in this case 10 (KE=1, KE=0).

[0040] Version 1a and version 1b may, for example, use the same versionnumber, since the only differences between them are in non-criticalelements.

[0041]FIG. 2 shows one possible implementation of expansions, when theseare possible only at the end of the previous versions.

[0042]FIG. 3 shows one possible implementation of expansions based onthe described method. In this case, the number of critical expansions isdefined by the number of leading bits that are set before the firstunset bit. The number of critical expansions is in this case equivalentto the number of mutually independent versions of the message. Asubscriber terminal which supports only version 1a may use versions 1 aand 1 b of the protocol. Version 1b may in this case possibly not beunderstood completely, but it can nevertheless be used on the basis ofthe non-critical expansions. Further codings, which will be familiar tothose skilled in the art, are feasible.

1. A method for signal transmission in a radio communications system, inwhich a message of a protocol is signaled to a subscriber terminal (UE)by a base station system (BSS) in the radio communications system, withthe message comprising at least one message element, characterized inthat changes from message elements in comparison to an older version ofthe message are signaled at the start of the message.
 2. The method asclaimed in claim 1, characterized in that the number of changes to themessage elements is in each case signaled.
 3. The method as claimed inclaim 2, characterized in that only the number of critical changes issignaled.
 4. The method as claimed in a preceding claim, characterizedin that the changes represent an expansion of the older message by newmessage elements, a removal of message elements, and/or a change tomessage elements.
 5. A method for signal transmission in a radiocommunications system, in which a message of a protocol is signaled to asubscriber terminal (UE) by a base station system (BSS) in the radiocommunications system, with the message comprising at least one messageelement, characterized in that the subscriber terminal (UE) signals thenumber of changes to message elements in comparison to an older versionof the message, which is known to it, to the base station system, andthe base station system (BSS) selects a version of the message which isknown to the subscriber terminal (UE) and signals this to the subscriberterminal (UE).
 6. The method as claimed in the preceding claim,characterized in that the subscriber terminal (UE) signals the maximumidentified number of changes in the message to the base station system(BSS).
 7. A method for signal transmission in a radio communicationssystem, in which a message of a protocol is signaled to a subscriberterminal (UE) by a base station system (BSS) in the radio communicationssystem, with the message comprising at least one message element,characterized in that the subscriber terminal (UE) signals a version ofthe message, which is known to it, to the base station system, and thebase station system (BSS) selects the signaled version of the messageand signals it to the subscriber terminal (UE).
 8. A base station system(BSS) in a radio communications system for carrying out the method asclaimed in claim 1, with the radio communications system being in theform of a mobile radio system or a wire-free subscriber access system.